1. Field of the Invention
This invention relates to a self-aligning roller bearing in which occurrence of edge stress on the surface of contact between rollers and track surfaces is eliminated or decreased.
2. Related Background Art
In the prior-art self-aligning roller bearing (see FIG. 5 of the accompanying drawings), contacts between an inner race 10 and rollers 30 and between an outer race 20 and the rollers 30 are contacts between single arcs when viewed in a plane containing the bus line of the roller 30. This leads to the following disadvantages:
(1) If the rate of contact between the arc of the bus line of the roller (radius of curvature R.sub.C) and the arcs of the bus lines of the track surface (the radius of curvature R.sub.B of the inner race and the radius of curvature R.sub.A of the outer race) is made great, as seen in the state of stress distribution on the surface of contact between the inner race 10 and the roller 30 show in FIG. 6 of the accompanying drawings, the stress in the end portions of contact sharply increases (edge stress occurs) with an increase in the load, and this results in the problems of a short life, abrasion, seizure, etc. PA1 (2) If the rate of contact between the arc of the bus line of the roller 30 and the arcs of the bus lines of the track surfaces is made small to avoid the occurrence of such edge stress, the range of the load in which a state of point contact is brought about increases, and this results in the problems of a short life, reduced rigidity, abrasion, etc. The state of stress distribution on the surface of contact between the outer race 20 and the roller 30 shown in FIG. 6 is that in the case where the rate of contact between the roller 30 and the outer race 20 has been made small. PA1 (3) When a decrease in the rotational torque of the bearing is contemplated by suitably selecting the rate of contact between the inner race and the rollers and the rate of contact between the outer race and rollers, the problem mentioned under item (1) or (2) above arises depending on the magnitude of the load and therefore, design is not easy.
A technique which solves the above-noted problems is disclosed in Japanese Laid-open Patent Application No. 60-175818. That is, it is shown in it that the bus line of one or both of the track surface of the inner race and the track surface of the outer race is formed by a curve comprising a plurality of radii of curvature and thereby edge stress can be decreased.
However, the actual application of the technique disclosed in the above-mentioned publication would leave some problems still left to be solved.
It is difficult in design and manufacture to properly form the curves of the track surfaces in conformity with the condition under which the bearing is used. Where the bus line of only one of the track surfaces is formed by a curve comprising a plurality of radii of curvature, unless the arc of the other track surface is properly designed, edge stress will increase on the other track surface side and the life of the bearing will become shorter. Also, where the track surface of the outer race is formed by a bus line using a curve comprising a plurality of radii of curvature, the position of contact between the outer race and the rollers will change due to the aligning property between the outer race and the rollers and thus, they will contact each other at other position than the original position of contact aiming at a long life and a high performance, and therefore the intended purposes cannot be achieved.
Thus, according to the technique disclosed in the above-mentioned publication, the purposes of decreasing edge stress and obtaining a long life of a self-aligning roller bearing cannot be fully achieved.